Catalyst compositions comprising metallocene complexes activated by alkylalumoxane activators (or cocatalysts), were introduced to the art of polymerization catalysis in the mid-1970s. Alkylalumoxanes exhibit several inherent problems in use, such a need for high [alumoxane]:[metallocene] ratios to produce highly active catalyst compositions, highly reactivity toward impurities (moisture, alcohols, etc.) and flammability. Accordingly, some of the developments in this area of catalysis involved a search for alternative cocatalysts capable of activating metallocene complexes.
The class of alkylalumoxanes comprises oligomeric linear and/or cyclic compounds represented by the formulas R--[Al(R)--O].sub.n --AlR.sub.2 for linear oligomeric alumoxanes and [--Al(R)--O].sub.n for cyclic oligomeric alumoxanes where R is a C.sub.1 -C.sub.8 alkyl group. If R is the methyl group, the compound is called methylalumoxane or MAO. MAO has been the most widely used cocatalyst in metallocene catalyst systems.
It is an object of this invention to obviate the use of MAO as a cocatalyst for metallocene complexes.